In a general conference or family meetings, a projector is usually used to project materials on a screen. Since the projector projects the materials on the screen via a light beam, the place of display is commonly a dark room so as to prevent interference from external light. The projection mechanism of the projectors is one of the methods currently often used by people to share their materials with others.
However, the length of the screen of the projector is commonly fixed or manually controlled. Since the distance of the projector from the screen affects the length of the screen, the length of the screen should be adjusted accordingly. Hence, a user usually needs to adjust the length of the screen manually, which is not convenient.
Therefore, how to control automatically the length of the projection screen directed to the problem discussed above to resolve the drawback of the conventional projection screen whose length needs to be adjusted manually and to allow the length of the projection screen to be controlled automatically or by a program has been desired by users and the inventor of the present invention for a long time. Hence, based on the practical experiences of research, development and sales of related products over the years, the inventor of the present invention tried his best to survey, design and research with his professional knowledge to solve the problem of the prior art. Eventually, the inventor figured out a method for automatically controlling the length of the projection screen that can resolve the problem described above and discloses the same below in detail.